Home convenience and protection equipment such as garage door operators, lighting systems and security systems are coming to be viewed as necessities and not merely luxuries. These systems are often controlled by transmitters providing a radio frequency signal carrying a code. For security, the code must be kept secret and must be one of a large number of possible codes. But for convenience, the transmitters and receivers they control should be simple to program with the code.
Various controller systems have been proposed and/or manufactured using digital radio control and digital system processing, and allowing codes to be established by the user or randomly generated. In one system, a unique code is established at the transmitter using a number of two-position switches The remote receiver also has a like number of switches to set the established code. For further information on the structure and operation of such a system, reference may be made to U.S. Pat. No. 29,525 to Willmott. In U.S Pat. No. 4,178,549 to Ledenbach et al., the receiver recognizes a received signal from being from a particular transmitter by measuring and comparing relative durations of the pulse and non-pulse time intervals.
Other systems have been proposed which do not require the user to set the code by operating switches on the transmitter and receiver. In one system, a random code generator at the receiver establishes the code. The new code is placed in the memory of a transmitter by holding the transmitter in proximity to the receiver which flashes the established code by means of a light emitting diode to a phototransistor in the transmitter. In another system, each transmitter has its own unique code. The receiver can learn up to five unique codes. Should a transmitter be lost or stolen, the code for that transmitter can easily be removed from the memory of the receiver. For further information concerning the structure and operation of such systems, reference may be made to U.S. Pat. Nos. 4,529,980 to Liotine et al., and 4,750,118 to Heitschel et al., respectively.